Tiffany is 28 years older than Luis. Nineteen years ago, Tiffany was 5 times as old as Luis. How old is Luis now?
Explanation: We can use the given information to write down two equations that describe the ages of Tiffany and Luis. Let Tiffany's current age be $t$ and Luis's current age be $l$ The information in the first sentence can be expressed in the following equation: $t = l + 28$ Nineteen years ago, Tiffany was $t - 19$ years old, and Luis was $l - 19$ years old. The information in the second sentence can be expressed in the following equation: $t - 19 = 5(l - 19)$ Now we have two independent equations, and we can solve for our two unknowns. Because we are looking for $l$ , it might be easiest to use our first equation for $t$ and substitute it into our second equation. Our first equation is: $t = l + 28$ . Substituting this into our second equation, we get the equation: $(l + 28)$ $-$ $19 = 5(l - 19)$ which combines the information about $l$ from both of our original equations. Simplifying both sides of this equation, we get: $l + 9 = 5 l - 95$ Solving for $l$ , we get: $4 l = 104$ $l = 26$.